Light conversion modules or light converters are configured to convert the wavelength or range of wavelengths of a light emission generated from a light source to another wavelength or range of wavelengths (i.e., a converted light emission). For example, a light conversion module such as a camera flash can include a light-emitting diode (LED) and a phosphor (e.g., Ce+:YAG). In some instances, the phosphor may be suspended in a matrix such as silicone or another polymer, wherein the matrix ideally maintains high optical transmittance over the lifetime of the phosphor or light conversion module. During operation of such a light conversion module, the LED generates a light emission of a particular wavelength. When the light emission illuminates the phosphor, the phosphor can generate a converted light emission of another wavelength or range of wavelengths. In some instances, the converted light emission may be more functionally suited or aesthetically pleasing than the light emission generated by the LED. For example, an LED may be configured to emit ultraviolet light, which is invisible to humans, onto a phosphor configured to convert the ultraviolet light to a longer wavelength (or range of wavelengths), which is visible to humans. Such a process has readily apparent implications for applications such as camera flashes, interior lighting, and automotive headlights. In some instances, light emissions characterized by shorter wavelengths, such as ultraviolet light, permit the use of a wider range of phosphors. Indeed, this can be a distinct advantage for various applications such as camera flashes, interior lighting, and automotive head-lighting.
Light conversion modules that use LEDs, however, experience a number of limitations. For example, LEDs are typically characterized by low optical power. Accordingly, a light conversion module would need to include a large volume of phosphor in order to achieve a desired optical output. Large phosphor volumes necessarily lead to a corresponding increase in the size (i.e., height and/or lateral footprint) of such a light conversion module.
Compared to LEDs, other light sources such as laser diodes can exhibit far greater optical power; however, laser diodes implemented in light conversion modules can present a number of significant challenges. For example, in some instances the optical power and heat generated by a laser diode could be sufficient to degrade the phosphor matrix thereby reducing the light conversion efficiency (i.e., quantum yield) of the phosphor or generating an undesirable chromatic shift in the converted light emission. Some of the aforementioned are well-established challenges observed in light conversion modules utilizing LEDs characterized by even moderately low optical power. Further, the aforementioned challenges can be particularly acute for light sources configured to emit ultraviolet light, wherein certain chemical bonds within the matrix molecules (e.g., the bonds in silicone to methyl functional groups) may be particularly susceptible to degradation. Finally, light sources with high optical power, such as laser diodes, may present a human eye-safety risk.